1. Field of the Invention
This invention relates generally to a tuning apparatus, and more particularly is directed to a novel tuning apparatus in which a function thereof, such as, a muting and/or automatic frequency control operation of the tuning apparatus, is controlled in dependence on the relation of the tuned broadcast frequency to one or more preset broadcast frequencies.
2. Description of the Prior Art
In a prior art radio receiver, inter-station noise is eliminated by providing a muting gate in a signal transmitting path and controlling such muting gate by a rectified output signal from an IF amplifier. An FM receiver is also well-known in which a DC output signal of an FM discriminator and a rectified output signal of the IF amplifier are both detected and a logic circuit controls the muting gate in response to both of such output signals. With a muting circuit of the foregoing type, the broadcast signal from any station received with a level higher than a predetermined value will be transmitted through the muting gate. In other words, the muting circuit is effective to eliminate only those broadcast signals received at levels below the predetermined value. By reason of the foregoing, the existing muting circuit does not facilitate the manipulation of a tuning apparatus for receiving signals from only a limited number of preselected stations in cases where the broadcast signals from many stations may be received at acceptable levels.
Although automatic tuning radio receivers of the .mu.-tuning type are available for receiving only the signals from specific broadcast stations, such .mu.-tuning type receivers are relatively complicated and expensive.
Furthermore, it has been known to provide a radio receiver with an automatic frequency control circuit (hereinafter referred to as an AFC circuit) in order to stabilize the receiving condition. However, when it is desired to receive the broadcast signal from only one of several stations that may be within the pull-in range of the AFC operation, the existing receiver does not afford a simple control for both the AFC operation and the muting operation.